This invention relates to multipurpose photographic film strip cassettes in which the exposed film strip contained in the cassette may be processed, viewed by projection and rewound automatically without removal from the cassette in accordance with information supplied by the condition of the cassette and the film strip contained therein. More particularly, it concerns an improved apparatus for releasing processing fluid from an initially sealed reservoir forming part of a film processing organization of such cassettes.
Multipurpose photographic film cassettes have been developed for use in cinematographic systems illustrated and described, for example, in U.S. Pat. No. 3,615,127 issued to Edwin H. Land on Oct. 26, 1971; U.S. Pat. No. 3,623,417 issued Nov. 30, 1971 to Vaito K. Eloranta; U.S. Pat. No. 3,785,725 issued Jan. 15, 1974 to John F. Batter et al.; U.S. Pat. No. 3,895,862 issued July 22, 1975 to Joseph E. Stella et al.; and in a copending application Ser. No. 756,425, filed by W. A. Holmes and D. T. Scholz on Jan. 3, 1977, all of which are owned by the assignee of the present invention.
In such systems, a strip of photographic film contained in a cassette can be exposed in a camera adapted to receive the cassette and then processed to provide viewable images by placing the cassette in a viewing apparatus equipped to activate a cassette contained processor upon rewinding the exposed film strip. After processing in this manner, the viewing apparatus is operated as a projector to advance the film incrementally frame by frame past the light source so that the scene to which the film was exposed is reproduced in a manner well-known in the motion picture art.
In systems of the type aforementioned, the processing operation after film exposure and before viewing entails the deposition of a uniform coating of processing fluid along the length of the film strip to effect a diffusion transfer of a negative image in a light sensitive emulsion layer on the film strip to a positive image receiving layer or interface. The processing fluid supply is contained in an initially closed reservoir or pod housed within the film cassette, the reservoir having a removable tear tab closure capable of being opened upon activation of the processor by the viewing apparatus to allow the fluid to escape from the pod and pass through a nozzle-like opening against the exposed emulsion layer on the film strip. Although the processor is operated only once in any single cassette which provides a permanent housing for the film strip therein, its operation to achieve a uniform and complete layer of processing fluid over the exposed emulsion layer on the film strip is vital to satisfactory operation of the overall system since any defect in the operation of the processor will result in undesirable and permanent blemishes plainly observable during projection of the processed film.
To ensure retention of the processing fluid in the cassette contained reservoir or pod up to the time it is needed for the processing operation, and also in some measure to ensure complete availability of the processing fluid upon initial activation of the processor, the processing fluid reservoir in such systems is provided with a relatively large opening covered initially by a releasably bonded tear tab closure capable of being completely peeled from the opening to release the processing fluid for distribution against the emulsion layer of the exposed film strip. In prior systems of the type mentioned above, the tear tab initially sealing the processing fluid reservoir extends from one end of the reservoir opening to the other at which it is folded back on itself.
As described in the above-noted U.S. Pat. No. 3,895,862, no viewer mounted or other external means is needed for effecting a release of processing fluid from the initially sealed storage reservoir to initiate a processing cycle automatically upon rewinding the film strip after exposure in the cassette. The release of processing fluid from the reservoir is brought about by a pull strip extension connected at one end to a folded back portion of the reservoir sealing tear tab and having at its free end, a configuration adapted to engage in an aperture formed in the trailing end portion of the film strip attached to the supply spool during initial rewind rotation of the supply spool. The pull strip, which may be mylar or other similar material having the physical characteristics of a photographic film strip, is initially supported and constrained to an essentially S-shaped tortuous path in which the intermediate leg is established by a channel formed by internal cassette walls. The pull strip accordingly extends initially upward in confronting relation with the tear tab, then makes a downward turn passing through the aforementioned channel and makes a second turn at the lower end thereof before exiting from the channel. At its exit from the channel, the extension is bent back on itself without exceeding the elastic limits of the material from which it is made so that the projecting free end lies yieldably against the outer convolutions of the film strip on the supply spool. As the film strip pays out from the supply spool during exposure, the free end of the pull strip will move inwardly due to the diminishing diameter of film strip convolutions on the supply spool until the film strip is completely exposed. At this time, an aperture in the supply spool connected trailing end portion of the film strip will have passed the free end of the pull strip extension so that upon rewinding of the film strip back onto the supply spool, a latching tongue at the free end of the pull strip will engage in the film strip aperture and become entrained between successive convolutions of the film strip supply spool trailing end portion. Continued rewind rotation of the supply spool will effect a pulling action on the pull strip causing it to advance through the S-shaped tortuous path and correspondingly, resulting in peeling of the tear tab closure from the processing fluid reservoir to release the processing fluid for application thereof to the exposed film strip. After having been peeled completely from the processing fluid reservoir, the tear tab is disengaged from the pull strip by a knife-like formation at the exit of the channel formed by the internal cassette walls. The removed tear tab closure will remain in a storage chamber defined by the channel once the processing cycle has been complete.
In order to assure reliable separation of the tear tab from the processing fluid reservoir, the cassette components and the viewer drive system must be capable of imparting a significant force upon the tear tab through the pull strip. Several design considerations arise from this requirement; one of such considerations being that all components involved in transmitting the necessary force must be sufficiently strong to do so without failing. A second consideration is that minimizing drag due to friction in the force transmitting chain of components will minimize the torque that the viewer's drive mechanism must be capable of imparting in order to effect tear tab release. The support of the pull strip at the two turning points of the S-shaped path has proved to be a particularly weak link in satisfying the above considerations.
Several configurations have been used to support the flexible pull strip at the turning points necessitated by the S-shaped path of the strip. As shown in the above-referenced U.S. Pat. No. 3,895,862, one approach has been a conventional roller arrangement wherein a roller is journalled upon an upstanding pin formed in the cassette wall. Another approach also illustrated in U.S. Pat. No. 3,895,862 is an enlarged radius portion formed integrally with one of the channel forming walls.
The journalled roller arrangements presents the obvious problem that the mounting pin is like a cantilevered beam with great stress occurring when under load at the lower end where it is attached to the cassette wall. Accordingly, a large pin is required to adequately support the roller when the pull strip is being advanced thereby to remove the tear tab. Further, the larger the mounting pin is made, the greater the frictional forces developed between the pin and the inside diameter of the roller. Such friction results in a reluctance of the roller to rotate thereby increasing the drag upon the pull strip as it passes therearound.
The use of the enlarged radius portion has the disadvantage that the pull strip experiences greater frictional drag than would be the case with a rotating support where rolling friction would be experienced.